The proposed research involves investigation of membrane electrical properties and contractile activation in single isolated smooth muscle cells from Amphiuma stomach. Electrophysiological analyses will utilize single-microelectrode current clamp and two-microelectrode voltage clamp techniques. The effects of extra- and intracellular Ca ions on membrane ionic currents will be investigated in detail using ion substitutions and pharmacological manipulation of membrane conductances. Voltage clamp techniques and Arsenazo III absorbance spectroscopy will be used to control and monitor intracellular Ca ion changes. These data will be related to contractile activation by direct measurement of single cell isometric tension under conditions shown by previous voltage clamp and spectroscopy measurements to produce intracellular Ca ion changes of known magnitude and time-course. It is expected that these studies will provide the basis for quantitative analysis of drug and hormone effects on this preparation. Modeling and simulation of these results will be oriented toward refinement of existing experimental protocols so that specific models of excitation and ECcoupling processes can be tested.